Die bonding is one of the key manufacturing processes in electronic packaging in which a semiconductor die singulated from a wafer is detached and picked from an adhesive dicing tape and then bonded onto a substrate, such as a copper leadframe or a printed wiring board (“PWB”) substrate.
During the die detachment part of the process, a die from a sawn wafer is detached from an adhesive dicing tape using a technique that involves the utilization of a single pin or a plurality of push-up pins for initiation and completion of the delamination of the die from the dicing tape with the cooperation of vacuum suction from a pick-up tool holding onto the dicing tape. This technique is commonly adopted for both die bonding and flip chip bonding processes.
In the development of high density electronic devices, semiconductor dice have become thinner and larger. It is a challenging task to detach a die from an adhesive dicing tape without damaging the die when the thickness of the die is reduced to below 200 microns or size of about 8×8 mm as the rigidity of the die is reduced and the chances of deformation of the die increase. Hence, an apparatus that is capable of reliably detaching thin and large dice from dicing tapes is becoming a critical component in electronic assembly equipment
FIG. 1 is a schematic cross-sectional view of a conventional die detachment tool 102 and a pick-up tool 104 of a die bonder 100. The die detachment tool 102 comprises an ejector 101 which includes an ejector chuck 106 and ejector pins 108 housed in an ejector cap 110. The pick-up tool 104 comprises a collet 112 and a collet shaft 114. An adhesive dicing tape 116 with dice 118 attached is located and held in contact with the surface of the ejector cap 110 by vacuum suction force provided from a vacuum channel 120 through vacuum holes located on the ejector cap 110. The die detachment tool 102 is driven vertically by an actuator.
Various pin assemblies have been implemented in the prior art to detach a die from an adhesive dicing tape. For a die of relatively small size such as 2×2 mm2, a single ejector pin may be positioned at the center of the die to be detached. A single ejector or push-up pin approach is illustrated in U.S. Pat. No. 5,755,373 entitled “Die Push-Up Device” which describes a push-up pin in the form of a needle, which is fastened to a holder for pushing the die so as to separate the die from the dicing tape held by vacuum suction provided by a vacuum assembly. The vacuum assembly is usually fixed in position and the push-up needle is independently movable by a raising-and-lowering motor driven mechanism. When the push-up pin reaches a certain height, the dicing tape is substantially delaminated from the die leaving only a small contact area supported by the pin. The adhesion of the die to the dicing tape is minimal, so that it is possible to lift the said die up from the dicing tape using a vacuum collet without damaging the die. However, as the size of the die increases in area and its thickness decreases, the single push-up pin approach will be inadequate for successful pick-up.
For larger dice and in particular thin dice, multiple ejector pins may be used in order to distribute a push-up force on the die and reduce the pinching effect from the ejector pins. A multiple ejector or push-up pins approach is illustrated in US publication number 2004/0115904 A1 entitled “Apparatus And Method for Thin Die Detachment” which discloses a plurality of ejector pins which partially detach a die from an adhesive surface for detachment by a collet. This is achieved by having each ejector pin contact and raise a second surface of the film opposite the adhesive surface at positions substantially at the corners of the die to be detached within a predetermined distance from the edges of the die.
Alternatively, a two-stage ejection approach illustrated in U.S. Pat. No. 4,850,780 entitled “Pre-Peel Die Ejector Apparatus” attempts to overcome the above problem by providing a telescopic ejector chuck. The telescopic ejector chuck comprises an outer housing surrounded by vacuum suction apertures for pre-peeling the die, and a central housing with a motorized ejector pin connected to an ejector collar for pushing the die away from the dicing tape so that the die is substantially detached from the dicing tape.
A disadvantage of this two-stage approach is the complex design of the vacuum-and-spring-loaded telescopic ejector chuck, so that its size has to be relatively large. With its size constraint, the ejector chuck is found to be only effective for die sizes larger than 5 mm. The apparatus is therefore not applicable to semiconductor devices with smaller die sizes. It would be desirable to devise a die detachment tool that is effective for delaminating both large and small dice.
Further, during die detachment, peeling energy is applied to a die which is being detached by the push-up motion of the ejector pins and the vacuum suction on the dicing tape in order to overcome the interfacial adhesion between the die and the dicing tape. The pinching effect by the ejector pins and the bending of the die may result in deformation of the die. Deformation and detachment are two opposing processes during the pick-up process. When the applied peeling energy reaches the critical interfacial adhesion strength, detachment of the die from the dicing tape will occur. However, the die will crack or break when the deformation of the die reaches the critical strength of the die. The critical strength of the die depends on various factors such as the material of the die, wafer thinning, the pattern on the surface of the die and die sawing quality.
For conventional die detachment using ejector pins, the pinching effect and bending deformation are affected by the number, arrangement and geometry of the ejector pins. For larger die sizes, the ejector pins located at the periphery of the die will also tend to inhibit propagation of delamination towards the center of the die. Furthermore, it is necessary to custom-make an ejector pin chuck to suit dice of various sizes so as to arrange the ejector pins in such a manner as to reduce the pinching effect and bending deformation. It would be desirable to overcome the drawbacks of current die detachment tools as described above.